Patent GB-599311-A (GB)
Title: Improvements in fluid pressure operated speed governing systems
IPC: G05D13/00
Filed: 1944-12-02
Abstract: 599,311. Fluid-pressure servomotor-control systems; valves. MASSEY MACHINE CO. Dec. 2, 1944, No. 24130. Convention date, Dec. 3, 1943. [Class 135] [Also in Group XXVI] A speed governor comprises a regulating member movable in response to pressure changes in a pressure chamber continuously supplied with pressure fluid and a valve movable by a speedresponsive element to control these pressure changes, the movement of the valve by the speed-responsive element being yieldably opposed by an adjustable fluid pressure. The latter pressure may be adjusted manually to alter the speed setting or by the movement of the regulating member to introduce " speed droop," i.e. adjustment of speed setting according to the load, or by changes in a further physical characteristic such as pressure or liquid level. As shown in Fig. 1, the regulating member comprises a piston 37 movable in a cylinder 36 against a spring 38 by pressure fluid such as oil supplied through conduits 27, 35 by a pump 23 driven through gears 24, 25 from a shaft 10, the speed of which is to be controlled. The shaft 10 has a resilient driving connection 14 with a hollow shaft 12 rotatable in a block 13 to which the conduits 27, 35 are connected. Within the shaft 12 is a slidable valve 16 controlling ports 30 through which pressure fluid from the conduits 27, 35 escapes to a sump 40, the fluid passing freely around the valve stem 15 to ports 42 in the shaft 12. The ports 30 may have parabolically flared parts to ensure a linear relation between the speed of the shaft 10 and the pressure in the cylinder 36. An annulus 43 connects the conduits 27, 35 permanently. The speed-responsive element comprises fly-weights 18 on arms 19 with a common pivot 20 on the shaft 12, the arms being connected to links 21 which have a common pivot 22 on the valve stem 15. The fly-weights are connected by a relatively light spring 44 which is unstressed in the neutral position of the mechanism. The spring 44 may be replaced by a tension and a compression spring, one inside the other. The major part of the centrifugal force passed on to the valve 16 is balanced by fluid pressure which has access to its underside through passages 31 fed from the conduit 27 and which is controlled, within a range determined by a manual valve 33, by a leak-off valve 41. The range of pressures to which the cylinder 36 may be subject is likewise adjustable by a manual valve 32. The conduit 27 contains an accumulator 26. The regulating piston 37 operates a shaft 11 connected to an, engine throttle valve or other fuel control means through a fluidpressure servomotor comprising a double-acting piston 47 in a cylinder 46 fed through passages 63, 64 controlled by a piston valve 50 connected by a lever 59 with an adjustable fulcrum 66 to the piston 37. The valve 50 is supplied from the pump 23 by a conduit 54 and moves within a slidable ported seat 53 which is adjusted so that it follows up the movement of the valve 50 and so brings the servo-piston 47 to rest by a compensating arrangement comprising a piston 68 movable in a cylinder 67 under the control of a piston valve 70 fed by the conduit 54. Valves 65, 84 manually control the speed of operation of the pistons 47, 68 respectively. The sleeve 53 is initially moved in the same direction as the valve 50 by the piston 47 which acts through its piston-rod 48, a lever 80 with an adjustable fulcrum 81. and a lever 78. The latter is pivotally connected to the lever 80, the piston 68 and a member 76 which moves the sleeve 53 and the valve 70 in unison. The piston 68 during this time is hydraulically locked in its cylinder. The movement of the valve 70, however, causes the piston 68 to move the sleeve 53 in the opposite direction to the original movement of the valve 50 and if the compensating device is properly adjusted, the sleeve 53 and the valve 50 return to their initial positions in synchronism. The fulcrum 66 adjusts the sensitivity of the governor and the fulcrum 81 adjusts the magnitude of the response of the piston 47 for a given change in speed. The speed setting of the governor is adjusted by adjustment of the leak-off valve 41 and this is effected, manually by an arm 90 acting through a linkage 87, 88, 89 involving a floating lever 88. The position of the shaft 11 or of the piston-rod 48 is an indication of the prevailing load and the speed-setting is adjusted according to the load by a lever 93 with an adjustable fulcrum 94, the lever being pivoted on the piston-rod 48 and connected by a link 92 to the floating lever 88. The fulcrum 94 moves in a slot in the lever 93 which may be carried beyond the connection with the link 92 to provide for negative speed droop. The governor mechanism only operates up to a predetermined maximum load limit, which is reached when a projection 98 on the piston-rod 48 engages a link 99 with an adjustable pivot 100 which link closes the piston valve 50 and stops further movement of the shaft 11. The valve 41 may also be adjusted in dependence upon pressure, e.g. in the case of systems involving engine-driven pumps or compressors where the engine is controlled according to its speed and according to the pressure delivered by the pump or compressor. In this case, the delivery pressure acts through a connection 117, Fig. 3, on a piston 116 floating on a column 118 of liquid, e.g. mercury, connected to another liquid column 113 supporting a spring-loaded piston 112 connected through a further floating lever 110 to the arm 90 and to the floating lever 88. The lever 110 in another form suitable for controlling the pump driving engine of a sewage plant is connected to a float. The governing mechanism may control a variable pitch propeller. The' complete governor may be arranged in a casing provided with dials to indicate " prevailing speed," "load limit and " speed droop," the various adjustments being made from outside the casing.